This patch is similar in spirit to the "IB/mlx4: Handle Ethernet L2
parameters for IP based GID addressing".  It handles the fact that IP
based RoCE gids don't store Ethernet L2 parameters, MAC and VLAN.

When building an address handle, instead of parsing the dgid to
get the MAC and VLAN, take them from the address handle attributes.

Cc: Naresh Gottumukkala <bgottumukkala@emulex.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>